Determining a reference dose parameter of a computed tomography imaging

ABSTRACT

In a method, a water equivalent diameter (abbreviated to WED) of a slice plane of an examination volume is received via an interface. In an embodiment, a noise level based on the water equivalent diameter is determined via a computer unit, the noise level being an upper threshold value for the noise of a CT image dataset. Furthermore a reference dose parameter is determined based on the noise level and the water equivalent diameter via the computer unit, the reference dose parameter corresponding to a first x-ray dose, which would be absorbed in the slice plane during a recording of a first CT image dataset of the examination volume upon the noise of the first CT image dataset corresponding to the noise level. Finally, the reference dose parameter is indirectly proportional to a power of the noise level.

PRIORITY STATEMENT

The present application hereby claims priority under 35 U.S.C. § 119 toEuropean patent application number EP17164992.4 filed Apr. 5, 2017, theentire contents of which are hereby incorporated herein by reference.

FIELD

At least one embodiment of the application is generally related to amethod of determining a reference dose parameter of a computertomography image; and/or parameter determination unit; and/or a computerreadable storage medium.

BACKGROUND

The aim in computed tomography imaging, as well as obtaining a goodimage quality, is also that the respective examination volume absorbs anx-ray dose that is as small as possible, since a high x-ray dose canlead to potential damage to parts of the examination volume. This aim isalso referred to as ALARA (an acronym for “as low as reasonablyachievable”).

In such cases, with an increasing x-ray dose, the noise in the resultingimage dataset generally decreases, whereby the image quality increases.Computed tomography imaging can thus be referred to as optimum when theimage quality is selected as just good enough, and thus when the x-raydose is just high enough to still make a unique diagnosis of theresulting image possible. It is therefore usual to include doseparameters, for planning and/or for evaluating computed tomographyimaging.

It is known that a dose parameter can be calculated in relation to anaxial slice plane of the examination volume based on an axial sliceimage and further recording parameters, for example by way of aMonte-Carlo simulation. Here however the x-ray dose can only becalculated after the computed tomography imaging, thus the x-ray dosehere is only a result of the computed tomography imaging. Furthermore,with this method, very many slice images must be transmitted andanalyzed, if the x-ray dose is to be determined in a larger region ofthe examination volume, moreover a large amount of computing time mustbe expended for this calculation.

It is further known that a dose parameter can be calculated based solelyon the recording parameters of a computed tomography imaging. Thiscalculation is done specifically only for a particular manufacturer ofcomputed tomography devices or even more specifically for only one typeof computed tomography device. This only enables the dose parametercalculated in each case to be compared with restrictions betweencomputed tomography devices of different manufacturers or betweendifferent types. Furthermore the dose parameter calculated in each caseis not tailored individually to the patient.

The disadvantages of the large volume of data and of the poorcomparability become evident above all when pan-device or pan-hospitalevaluations of the dose parameter are to be carried out by way of anenvironment for distributed computing (a Cloud), wherein image dataand/or examination data must be stored geographically separated by anevaluation unit and therefore data transmission must take place. Atypical problem definition of such an evaluation is comparing the x-raydose absorbed by the patient for specific computed tomography imaging(of the head for example) with the national average. For this doseparameters for various device types must be calculated from data that isstored in different geographical locations by the evaluation unit.Furthermore the necessary data must also be accessible for theevaluation unit.

SUMMARY

At least one embodiment of the present invention provides a method ofcalculating the x-ray dose of a computed tomography imaging so that itcan be compared independently of the result of the computed tomographyimaging, in a rapid manner and without the transmission of large volumesof data.

At least one embodiment is directed to a method for determining areference dose parameter of a computed tomography imaging; at least oneembodiment is directed to a parameter determination unit; at least oneembodiment is directed to a computed tomography device; at least oneembodiment is directed to a computer program product; and at least oneembodiment is directed to a computer-readable storage medium.

Embodiment are described below both in relation to the devices and alsoin relation to the method. Features, advantages or alternate forms ofembodiment mentioned here are likewise also to be transferred to theother embodiments and vice versa. In other words the physical claims(which are directed to a device for example) can also be developed withthe claims that are described or claimed in conjunction with a method.The corresponding functional features of embodiments of the method inthis case are embodied by corresponding physical modules.

At least one embodiment of the inventive method for determination of areference dose parameter of a computed tomography imaging is based on awater equivalent diameter (abbreviated to WED) of a slice plane of anexamination volume being received via an interface. Furthermore a noiselevel based on the water equivalent diameter is determined via acomputer unit, wherein the noise level is an upper threshold value forthe noise of a CT image dataset. Furthermore a reference dose parameteris determined based on the noise level and the water equivalent diametervia the computer unit, wherein the reference dose parameter correspondsto a first x-ray dose that would be absorbed during a recording of afirst CT image dataset of the examination volume in the slice plane ifthe noise of the first CT image dataset corresponds to the noise level,and wherein the reference dose parameter is indirectly proportional to apower of the noise level. In other words, it is not necessary duringthis determination actually to record the first CT image dataset, thefirst x-ray dose is only theoretically absorbed in the slice plane, ifwhen using the recording parameter a first CT image dataset examinationvolume were to be recorded via the computed tomography device.

At least one embodiment of the invention further relates to a parameterdetermination unit, comprising the following units:

An interface, embodied for first receipt of a water equivalent diameterof a slice plane of an examination volume,

A computer unit, embodied for first determination of a noise level basedon the water equivalent diameter, wherein the noise level is an upperthreshold value for the noise of a CT image dataset,

further embodied for second determination of a reference dose parameterbased on the noise level and the water equivalent diameter, wherein thereference dose parameter corresponds to a first x-ray dose, which wouldbe absorbed during a recording of a first CT image dataset of theexamination volume in the slice plane, if the noise of the first CTimage dataset corresponds to the noise level, wherein the reference doseparameter is indirectly proportional to a power of the noise level.

At least one embodiment of the invention further relates to a computedtomography device comprising at least one embodiment of the parameterdetermination unit. A computed tomography device is embodied inparticular to create a tomographic slice image or a three-dimensionalimage of an examination volume by way of x-ray radiation.

At least one embodiment of the invention also relates to a computerprogram product with a computer program and also to a computer-readablemedium. A largely software-based realization has the advantage thatparameter determination units also used previously can be upgraded in asimple manner by a software update, in order to work in the inventiveway. Such a computer program product can, as well as the computerprogram, if necessary comprise additional elements, such as e.g.documentation and/or additional components, as well as hardwarecomponents, such as e.g. hardware keys (dongles etc.) for use of thesoftware.

At least one embodiment of the inventive method for determination of areference dose parameter of a computed tomography imaging, comprises:

receiving, via an interface, a water equivalent diameter of a sliceplane of an examination volume;

determining, via a computer unit, a noise level based on the waterequivalent diameter, the noise level being an upper threshold value fornoise of a CT image dataset;

determining, via the computer unit, a reference dose parameter based onthe noise level determined and the water equivalent diameter, thereference dose parameter corresponding to a first x-ray dose, absorbablein the slice plane during a recording of a first CT image dataset of theexamination volume upon noise of the first CT image datasetcorresponding to the noise level determined.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described and explained in greater detail belowwith reference to the example embodiments shown in the figures as wellas with reference to dummy code.

In the figures

FIG. 1 shows a flow diagram of a first example embodiment fordetermination of a reference dose parameter,

FIG. 2 shows a flow diagram of a second example embodiment fordetermination of a reference dose parameter,

FIG. 3 shows a flow diagram of a third example embodiment fordetermination of a reference dose parameter,

FIG. 4 shows a parameter determination unit,

FIG. 5 shows a parameter determination unit in an environment fordistributed computing.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

The drawings are to be regarded as being schematic representations andelements illustrated in the drawings are not necessarily shown to scale.Rather, the various elements are represented such that their functionand general purpose become apparent to a person skilled in the art. Anyconnection or coupling between functional blocks, devices, components,or other physical or functional units shown in the drawings or describedherein may also be implemented by an indirect connection or coupling. Acoupling between components may also be established over a wirelessconnection. Functional blocks may be implemented in hardware, firmware,software, or a combination thereof.

Various example embodiments will now be described more fully withreference to the accompanying drawings in which only some exampleembodiments are shown. Specific structural and functional detailsdisclosed herein are merely representative for purposes of describingexample embodiments. Example embodiments, however, may be embodied invarious different forms, and should not be construed as being limited toonly the illustrated embodiments. Rather, the illustrated embodimentsare provided as examples so that this disclosure will be thorough andcomplete, and will fully convey the concepts of this disclosure to thoseskilled in the art. Accordingly, known processes, elements, andtechniques, may not be described with respect to some exampleembodiments. Unless otherwise noted, like reference characters denotelike elements throughout the attached drawings and written description,and thus descriptions will not be repeated. The present invention,however, may be embodied in many alternate forms and should not beconstrued as limited to only the example embodiments set forth herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions,layers, and/or sections, these elements, components, regions, layers,and/or sections, should not be limited by these terms. These terms areonly used to distinguish one element from another. For example, a firstelement could be termed a second element, and, similarly, a secondelement could be termed a first element, without departing from thescope of example embodiments of the present invention. As used herein,the term “and/or,” includes any and all combinations of one or more ofthe associated listed items. The phrase “at least one of” has the samemeaning as “and/or”.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below,” “beneath,” or“under,” other elements or features would then be oriented “above” theother elements or features. Thus, the example terms “below” and “under”may encompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly. Inaddition, when an element is referred to as being “between” twoelements, the element may be the only element between the two elements,or one or more other intervening elements may be present.

Spatial and functional relationships between elements (for example,between modules) are described using various terms, including“connected,” “engaged,” “interfaced,” and “coupled.” Unless explicitlydescribed as being “direct,” when a relationship between first andsecond elements is described in the above disclosure, that relationshipencompasses a direct relationship where no other intervening elementsare present between the first and second elements, and also an indirectrelationship where one or more intervening elements are present (eitherspatially or functionally) between the first and second elements. Incontrast, when an element is referred to as being “directly” connected,engaged, interfaced, or coupled to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between,” versus “directly between,” “adjacent,” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments of the invention. As used herein, the singular forms “a,”“an,” and “the,” are intended to include the plural forms as well,unless the context clearly indicates otherwise. As used herein, theterms “and/or” and “at least one of” include any and all combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes,” and/or“including,” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist. Also, the term “exemplary” is intended to refer to an example orillustration.

When an element is referred to as being “on,” “connected to,” “coupledto,” or “adjacent to,” another element, the element may be directly on,connected to, coupled to, or adjacent to, the other element, or one ormore other intervening elements may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to,”“directly coupled to,” or “immediately adjacent to,” another elementthere are no intervening elements present.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Before discussing example embodiments in more detail, it is noted thatsome example embodiments may be described with reference to acts andsymbolic representations of operations (e.g., in the form of flowcharts, flow diagrams, data flow diagrams, structure diagrams, blockdiagrams, etc.) that may be implemented in conjunction with units and/ordevices discussed in more detail below. Although discussed in aparticularly manner, a function or operation specified in a specificblock may be performed differently from the flow specified in aflowchart, flow diagram, etc. For example, functions or operationsillustrated as being performed serially in two consecutive blocks mayactually be performed simultaneously, or in some cases be performed inreverse order. Although the flowcharts describe the operations assequential processes, many of the operations may be performed inparallel, concurrently or simultaneously. In addition, the order ofoperations may be re-arranged. The processes may be terminated whentheir operations are completed, but may also have additional steps notincluded in the figure. The processes may correspond to methods,functions, procedures, subroutines, subprograms, etc.

Specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments of thepresent invention. This invention may, however, be embodied in manyalternate forms and should not be construed as limited to only theembodiments set forth herein.

Units and/or devices according to one or more example embodiments may beimplemented using hardware, software, and/or a combination thereof. Forexample, hardware devices may be implemented using processing circuitrysuch as, but not limited to, a processor, Central Processing Unit (CPU),a controller, an arithmetic logic unit (ALU), a digital signalprocessor, a microcomputer, a field programmable gate array (FPGA), aSystem-on-Chip (SoC), a programmable logic unit, a microprocessor, orany other device capable of responding to and executing instructions ina defined manner. Portions of the example embodiments and correspondingdetailed description may be presented in terms of software, oralgorithms and symbolic representations of operation on data bits withina computer memory. These descriptions and representations are the onesby which those of ordinary skill in the art effectively convey thesubstance of their work to others of ordinary skill in the art. Analgorithm, as the term is used here, and as it is used generally, isconceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of optical, electrical, or magnetic signals capable of beingstored, transferred, combined, compared, and otherwise manipulated. Ithas proven convenient at times, principally for reasons of common usage,to refer to these signals as bits, values, elements, symbols,characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” of “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computingdevice/hardware, that manipulates and transforms data represented asphysical, electronic quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

In this application, including the definitions below, the term ‘module’or the term ‘controller’ may be replaced with the term ‘circuit.’ Theterm ‘module’ may refer to, be part of, or include processor hardware(shared, dedicated, or group) that executes code and memory hardware(shared, dedicated, or group) that stores code executed by the processorhardware.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

Software may include a computer program, program code, instructions, orsome combination thereof, for independently or collectively instructingor configuring a hardware device to operate as desired. The computerprogram and/or program code may include program or computer-readableinstructions, software components, software modules, data files, datastructures, and/or the like, capable of being implemented by one or morehardware devices, such as one or more of the hardware devices mentionedabove. Examples of program code include both machine code produced by acompiler and higher level program code that is executed using aninterpreter.

For example, when a hardware device is a computer processing device(e.g., a processor, Central Processing Unit (CPU), a controller, anarithmetic logic unit (ALU), a digital signal processor, amicrocomputer, a microprocessor, etc.), the computer processing devicemay be configured to carry out program code by performing arithmetical,logical, and input/output operations, according to the program code.Once the program code is loaded into a computer processing device, thecomputer processing device may be programmed to perform the programcode, thereby transforming the computer processing device into a specialpurpose computer processing device. In a more specific example, when theprogram code is loaded into a processor, the processor becomesprogrammed to perform the program code and operations correspondingthereto, thereby transforming the processor into a special purposeprocessor.

Software and/or data may be embodied permanently or temporarily in anytype of machine, component, physical or virtual equipment, or computerstorage medium or device, capable of providing instructions or data to,or being interpreted by, a hardware device. The software also may bedistributed over network coupled computer systems so that the softwareis stored and executed in a distributed fashion. In particular, forexample, software and data may be stored by one or more computerreadable recording mediums, including the tangible or non-transitorycomputer-readable storage media discussed herein.

Even further, any of the disclosed methods may be embodied in the formof a program or software. The program or software may be stored on anon-transitory computer readable medium and is adapted to perform anyone of the aforementioned methods when run on a computer device (adevice including a processor). Thus, the non-transitory, tangiblecomputer readable medium, is adapted to store information and is adaptedto interact with a data processing facility or computer device toexecute the program of any of the above mentioned embodiments and/or toperform the method of any of the above mentioned embodiments.

Example embodiments may be described with reference to acts and symbolicrepresentations of operations (e.g., in the form of flow charts, flowdiagrams, data flow diagrams, structure diagrams, block diagrams, etc.)that may be implemented in conjunction with units and/or devicesdiscussed in more detail below. Although discussed in a particularlymanner, a function or operation specified in a specific block may beperformed differently from the flow specified in a flowchart, flowdiagram, etc. For example, functions or operations illustrated as beingperformed serially in two consecutive blocks may actually be performedsimultaneously, or in some cases be performed in reverse order.

According to one or more example embodiments, computer processingdevices may be described as including various functional units thatperform various operations and/or functions to increase the clarity ofthe description. However, computer processing devices are not intendedto be limited to these functional units. For example, in one or moreexample embodiments, the various operations and/or functions of thefunctional units may be performed by other ones of the functional units.Further, the computer processing devices may perform the operationsand/or functions of the various functional units without sub-dividingthe operations and/or functions of the computer processing units intothese various functional units.

Units and/or devices according to one or more example embodiments mayalso include one or more storage devices. The one or more storagedevices may be tangible or non-transitory computer-readable storagemedia, such as random access memory (RAM), read only memory (ROM), apermanent mass storage device (such as a disk drive), solid state (e.g.,NAND flash) device, and/or any other like data storage mechanism capableof storing and recording data. The one or more storage devices may beconfigured to store computer programs, program code, instructions, orsome combination thereof, for one or more operating systems and/or forimplementing the example embodiments described herein. The computerprograms, program code, instructions, or some combination thereof, mayalso be loaded from a separate computer readable storage medium into theone or more storage devices and/or one or more computer processingdevices using a drive mechanism. Such separate computer readable storagemedium may include a Universal Serial Bus (USB) flash drive, a memorystick, a Blu-ray/DVD/CD-ROM drive, a memory card, and/or other likecomputer readable storage media. The computer programs, program code,instructions, or some combination thereof, may be loaded into the one ormore storage devices and/or the one or more computer processing devicesfrom a remote data storage device via a network interface, rather thanvia a local computer readable storage medium. Additionally, the computerprograms, program code, instructions, or some combination thereof, maybe loaded into the one or more storage devices and/or the one or moreprocessors from a remote computing system that is configured to transferand/or distribute the computer programs, program code, instructions, orsome combination thereof, over a network. The remote computing systemmay transfer and/or distribute the computer programs, program code,instructions, or some combination thereof, via a wired interface, an airinterface, and/or any other like medium.

The one or more hardware devices, the one or more storage devices,and/or the computer programs, program code, instructions, or somecombination thereof, may be specially designed and constructed for thepurposes of the example embodiments, or they may be known devices thatare altered and/or modified for the purposes of example embodiments.

A hardware device, such as a computer processing device, may run anoperating system (OS) and one or more software applications that run onthe OS. The computer processing device also may access, store,manipulate, process, and create data in response to execution of thesoftware. For simplicity, one or more example embodiments may beexemplified as a computer processing device or processor; however, oneskilled in the art will appreciate that a hardware device may includemultiple processing elements or processors and multiple types ofprocessing elements or processors. For example, a hardware device mayinclude multiple processors or a processor and a controller. Inaddition, other processing configurations are possible, such as parallelprocessors.

The computer programs include processor-executable instructions that arestored on at least one non-transitory computer-readable medium (memory).The computer programs may also include or rely on stored data. Thecomputer programs may encompass a basic input/output system (BIOS) thatinteracts with hardware of the special purpose computer, device driversthat interact with particular devices of the special purpose computer,one or more operating systems, user applications, background services,background applications, etc. As such, the one or more processors may beconfigured to execute the processor executable instructions.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective-C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

Further, at least one embodiment of the invention relates to thenon-transitory computer-readable storage medium including electronicallyreadable control information (processor executable instructions) storedthereon, configured in such that when the storage medium is used in acontroller of a device, at least one embodiment of the method may becarried out.

The computer readable medium or storage medium may be a built-in mediuminstalled inside a computer device main body or a removable mediumarranged so that it can be separated from the computer device main body.The term computer-readable medium, as used herein, does not encompasstransitory electrical or electromagnetic signals propagating through amedium (such as on a carrier wave); the term computer-readable medium istherefore considered tangible and non-transitory. Non-limiting examplesof the non-transitory computer-readable medium include, but are notlimited to, rewriteable non-volatile memory devices (including, forexample flash memory devices, erasable programmable read-only memorydevices, or a mask read-only memory devices); volatile memory devices(including, for example static random access memory devices or a dynamicrandom access memory devices); magnetic storage media (including, forexample an analog or digital magnetic tape or a hard disk drive); andoptical storage media (including, for example a CD, a DVD, or a Blu-rayDisc). Examples of the media with a built-in rewriteable non-volatilememory, include but are not limited to memory cards; and media with abuilt-in ROM, including but not limited to ROM cassettes; etc.Furthermore, various information regarding stored images, for example,property information, may be stored in any other form, or it may beprovided in other ways.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. Shared processor hardware encompasses asingle microprocessor that executes some or all code from multiplemodules. Group processor hardware encompasses a microprocessor that, incombination with additional microprocessors, executes some or all codefrom one or more modules. References to multiple microprocessorsencompass multiple microprocessors on discrete dies, multiplemicroprocessors on a single die, multiple cores of a singlemicroprocessor, multiple threads of a single microprocessor, or acombination of the above.

Shared memory hardware encompasses a single memory device that storessome or all code from multiple modules. Group memory hardwareencompasses a memory device that, in combination with other memorydevices, stores some or all code from one or more modules.

The term memory hardware is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium is therefore considered tangible and non-transitory. Non-limitingexamples of the non-transitory computer-readable medium include, but arenot limited to, rewriteable non-volatile memory devices (including, forexample flash memory devices, erasable programmable read-only memorydevices, or a mask read-only memory devices); volatile memory devices(including, for example static random access memory devices or a dynamicrandom access memory devices); magnetic storage media (including, forexample an analog or digital magnetic tape or a hard disk drive); andoptical storage media (including, for example a CD, a DVD, or a Blu-rayDisc). Examples of the media with a built-in rewriteable non-volatilememory, include but are not limited to memory cards; and media with abuilt-in ROM, including but not limited to ROM cassettes; etc.Furthermore, various information regarding stored images, for example,property information, may be stored in any other form, or it may beprovided in other ways.

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

Although described with reference to specific examples and drawings,modifications, additions and substitutions of example embodiments may bevariously made according to the description by those of ordinary skillin the art. For example, the described techniques may be performed in anorder different with that of the methods described, and/or componentssuch as the described system, architecture, devices, circuit, and thelike, may be connected or combined to be different from theabove-described methods, or results may be appropriately achieved byother components or equivalents.

At least one embodiment of the inventive method for determination of areference dose parameter of a computed tomography imaging is based on awater equivalent diameter (abbreviated to WED) of a slice plane of anexamination volume being received via an interface. Furthermore a noiselevel based on the water equivalent diameter is determined via acomputer unit, wherein the noise level is an upper threshold value forthe noise of a CT image dataset. Furthermore a reference dose parameteris determined based on the noise level and the water equivalent diametervia the computer unit, wherein the reference dose parameter correspondsto a first x-ray dose that would be absorbed during a recording of afirst CT image dataset of the examination volume in the slice plane ifthe noise of the first CT image dataset corresponds to the noise level,and wherein the reference dose parameter is indirectly proportional to apower of the noise level. In other words, it is not necessary duringthis determination actually to record the first CT image dataset, thefirst x-ray dose is only theoretically absorbed in the slice plane, ifwhen using the recording parameter a first CT image dataset examinationvolume were to be recorded via the computed tomography device.

The inventor has recognized that the noise level can be determined as anupper threshold value for the noise of a CT image dataset especiallyefficiently and quickly based on the water equivalent diameter. Theinventor has further recognized that both the water equivalent diameterand also the noise level can be used especially efficiently to determinethe reference dose parameter, since with the proposed method no largevolumes of image data must be transmitted, but also at the same timeallowing influences of the nature of the examination region to beincluded in the determination. In particular the water equivalentdiameter of the examination volume (for example of a patient) reflectsthe physical circumstances of the examination volume in relation to theslice plane, in particular better than in the calculation of thereference dose parameter based on statistical data not related to therespective examination region and/or to the respective patient. Theinventor has further recognized that the reference dose parameter,independent of manufacturer of a computed tomography device, isindirectly proportional to a power of the noise level, therefore thereference dose parameter can be determined in particular without usingan axial slice image and also independent of manufacturer.

According to a further embodiment of the invention the power has a valueof between 0.1 and 2.5, in particular of between 0.5 and 1.5, inparticular of between 0.9 and 1.1. In particular the power can have avalue of precisely 1. The inventor has recognized that by choosing sucha value the reference dose parameter can be determined especiallyprecisely.

According to a further embodiment of the invention the reference doseparameter is further proportional to an exponential function of thewater equivalent diameter. The inventor has recognized that thefunctional dependency of the reference dose parameter on the waterequivalent diameter can be described especially well and precisely by anexponential function.

According to a further embodiment of the invention the argument of theexponential function comprises the product of the linear attenuationcoefficient of x-ray radiation in water with the water equivalentdiameter. The inventor has recognized that the linear attenuationcoefficient of water also has an influence on the size of the referencedose parameter, and the common functional dependency of the referencedose parameter on the linear attenuation coefficient and on the waterequivalent diameter can be described especially well and precisely by anexponential function of the product of the two variables. Here theargument of a function describes the value from the definition volume ofthe function, which is used in the function in order to determine theassociated function value. Another word for argument of a function isindependent variable of the function. The linear attenuation coefficientof x-ray radiation in water is in particular a length, so that theintensity of x-ray radiation falls to a share of 1/e (1/e≈0.368) of theoriginal intensity when the x-ray radiation passes through water on apath with this length, wherein e (e≈2.718) refers to the Euler numberhere. In particular the exponential function involves an exponentialfunction for the basis of the Euler number e. 0.19 cm-1 is known inparticular as the linear attenuation coefficient of x-ray radiation inwater. Absorption coefficient is also known as a synonym for linearattenuation coefficient.

According to a further embodiment of the invention the reference doseparameter is the product of a proportionality constant with the quotientof the exponential function and the power of the noise level, wherein pis the value of the power, wherein the proportionality constant amountsto between 0.2 mGy·HUp and 2.0 mGy·HUp, or wherein the proportionalityconstant in particular amounts to between 0.5 mGy·HUp and 1.5 mGy·HUp,or wherein the proportionality constant in particular amounts to between1.2 mGy·HUp and 1.2 mGy·HUp. Here mGy·HUp refers to the unit Milligraymultiplied by Hounsfield unit to the power p. Here the unit one Gray isdefined in particular as one Joule per kilogram, and the Hounsfield unitis in particular the unit of the CT number. The inventor has recognizedthat by the choice of such a proportionality constant the reference doseparameter can be determined especially well and precisely.

According to a further embodiment of the invention, the noise level is apiecewise linear function of the water equivalent diameter. The inventorhas recognized that through this functional dependency the noise levelcan be determined especially well as a function of the water equivalentdiameter. A function is in particular piecewise linear when the secondderivation of the function at each point is either zero or is notdefined.

According to a further embodiment of the invention, the noise level is aconstant, sectionally defined function of the water equivalent diameterwith precisely two sections, wherein the first section is a constantfunction and wherein the second section is a linear function of thewater equivalent diameter. The inventor has recognized that through thisfunctional dependency the noise level can be determined especially wellas a function of the water equivalent diameter. In particular the firstsection comprises smaller water equivalent diameters than the secondsection.

The noise level s can be expressed in particular by the formula s=max(c,m·WED−t), wherein the variables c, m and t are constants. The constant ccan be chosen in particular as between 0 HU and 10 HU, in particular asbetween 2 HU and 6 HU or in particular as between 3 HU and 5 HU,furthermore the constant c can be chosen in particular as 4 HU. Theconstant m can be chosen in particular as between 0.5 HU/cm and 3 HU/cm,in particular as between 0.5 HU/cm and 2 HU/cm, in particular as between0.75 HU/cm and 1.25 HU/cm, in particular the constant m can also bechosen as 1.0 HU/cm. The constant t can be chosen as between 0 HU and 30HU, in particular as between 10 HU and 20 HU, in particular as between12 HU and 16 HU, but the constant t can also in particular be chosen as14 HU. The inventor has recognized that by such a choice of one or moreof the constants the dependence of the noise levels on the waterequivalent diameter can be described especially well.

According to a further embodiment of the invention, a size-specific doseestimation, abbreviated to SSDE, based on the reference dose parametercan further be determined via the computer unit. In particular thesize-specific dose estimation is calculated as a product of thereference dose parameter with a function, wherein the function dependson the water equivalent diameter, but not on the reference doseparameter. The function can in particular allocate a correction factorto a water equivalent parameter. The function can in this case inparticular be given as a table, wherein the table allocates a pluralityof water equivalent diameters to a correction factor in each case, andwherein function values for non-tabulated water equivalent diameters aredetermined by interpolation, in particular by linear interpolation. Theinventor has recognized that the size-specific dose estimation can becalculated especially well and precisely in this way on the basis of thereference dose parameter.

According to a further embodiment of the invention, a recordingparameter of a computed tomography device is determined via the computerunit based on the reference dose parameter, wherein a second x-ray dosecorresponds to the reference dose parameter, wherein the second x-raydose would be absorbed during recording of a second CT image dataset inthe slice plane if the second CT image dataset is recorded using therecording parameter by way of the computed tomography device. In otherwords it is not necessary here actually to record the second CT imagedataset, the second x-ray dose is only theoretically absorbed in theslice plane if, using the recording parameter, a second CT image datasetwould be recorded by way of the computed tomography device. Inparticular the recording parameter can also furthermore be based on thewater equivalent diameter.

Optionally in this embodiment of the invention, the determination of thesecond CT image dataset can also be recorded subsequently via thecomputed tomography device. The inventor has recognized that by thismethod step a recording parameter can be determined especiallyefficiently and easily, so that the second x-ray dose lies as close aspossible to the reference dose parameter, and thus the patient issubjected to an x-ray dose that is as small as possible. In particularin this way the recording parameters can be determined before the actualexamination. A recording parameter can for example involve the x-rayvoltage of the x-ray tubes, or the x-ray current of the x-ray tubes, orthe slice thickness of the second CT image dataset, or the pitch factorof a spiral recording, or further known parameters of computedtomography.

According to a further possible embodiment of the invention, a planningexamination volume is furthermore received via the interface. Theplanning examination volume can in particular describe the examinationvolume to be recorded during the first CT image dataset. Furthermore,based on the reference dose parameter, a planning dose parameter can becalculated via the computer unit, wherein an x-ray dose absorbed in theplanning examination volume corresponds to the planning dose parameter,if a CT image dataset of the planning examination volume is recorded,wherein the noise of the CT image dataset of the planning examinationvolume corresponds to the noise level. Furthermore the planning doseparameter can be displayed. The planning dose parameter can inparticular involve a dose length product. The inventor has recognizedthat, based on the planning dose parameter, there can be an especiallyeffective and precise planning of a computed tomography examination.

According to a further embodiment of the invention, a real doseparameter of a recording of a third CT image dataset of the examinationvolume is furthermore received via the interface. Furthermore, based ona comparison of the reference dose parameter and the real doseparameter, the power and/or the proportionality constant is correctedvia the computer unit. The inventor has recognized that through thecorrection based on such a comparison, the proportionality constant canbe corrected especially quickly and simply. This can be used inparticular to determine or to optimize the proportionality constant forvarious computed tomography products, in particular for various computedtomography products of different manufacturers.

At least one embodiment of the invention further relates to a parameterdetermination unit, comprising the following units:

An interface, embodied for first receipt of a water equivalent diameterof a slice plane of an examination volume,

A computer unit, embodied for first determination of a noise level basedon the water equivalent diameter, wherein the noise level is an upperthreshold value for the noise of a CT image dataset,

further embodied for second determination of a reference dose parameterbased on the noise level and the water equivalent diameter, wherein thereference dose parameter corresponds to a first x-ray dose, which wouldbe absorbed during a recording of a first CT image dataset of theexamination volume in the slice plane, if the noise of the first CTimage dataset corresponds to the noise level, wherein the reference doseparameter is indirectly proportional to a power of the noise level.

Such a parameter determination unit can be embodied in particular tocarry out embodiments of the inventive method described above. Theparameter determination unit is embodied to carry out this method andits embodiments, in that the interface and the computer unit areembodied to carry out the corresponding method steps.

At least one embodiment of the invention further relates to a computedtomography device comprising at least one embodiment of the parameterdetermination unit. A computed tomography device is embodied inparticular to create a tomographic slice image or a three-dimensionalimage of an examination volume by way of x-ray radiation.

At least one embodiment of the invention also relates to a computerprogram product with a computer program and also to a computer-readablemedium. A largely software-based realization has the advantage thatparameter determination units also used previously can be upgraded in asimple manner by a software update, in order to work in the inventiveway. Such a computer program product can, as well as the computerprogram, if necessary comprise additional elements, such as e.g.documentation and/or additional components, as well as hardwarecomponents, such as e.g. hardware keys (dongles etc.) for use of thesoftware.

A water equivalent diameter of a patient describes the overallattenuation of x-ray radiation by the patient standardized to theattenuation of water. A water equivalent diameter of a patient can bedefined in particular as the diameter of a water cylinder, wherein thewater cylinder, during computed a tomography imaging causes the sameoverall attenuation of the x-ray intensity as the patient, if the sliceplane of the axial slice images is arranged orthogonally to the axis ofsymmetry of the water cylinder. The water equivalent diameter can alsobe direction-dependent, in particular since the cross-section of apatient is not generally circular in shape. One method for calculatingthe water equivalent diameter on the basis of an axial slice image isknown for example from the publication American Association ofPhysicists in Medicine (2014): “Use of Water Equivalent Diameter forCalculating patient Size and Size-Specific Dose Estimates (SSDE) in CT(Task Group 220)”, the entire contents of which are hereby incorporatedherein by reference. Furthermore the water equivalent diameter can alsobe calculated on the basis of a topogram, for example by a thresholdvalue segmentation along a straight line.

A reference dose parameter and/or a real dose parameter can correspondin particular to a computed tomography dose index, abbreviated to CTDI,in particular to a weighted computed tomography dose index, abbreviatedto CTDIw, in particular to the volume-related computed tomography doseindex, abbreviated to CTDIvol, of a spiral computed tomography.

The computed tomography dose index (abbreviated to CTDI) can be definedvia the formula

${{CTDI} = {\frac{1}{nT}{\int_{{- 7}\; T}^{7\; T}{{D(z)}{dz}}}}},$

wherein T is the slice thickness of the computed tomography recording, nis the number of slices and D(z) is the dose measured at a location z byway of dosimeter in a phantom. Usually a phantom with diameter 16 cm orwith diameter 32 cm is used here. Usually the measurement is carried outwith a 100 mm long pin chamber dosimeter, and the definition of the CTDIis modified as

${CTDI}_{100} = {\frac{1}{nT}{\int_{{- 50}\mspace{14mu} {mm}}^{50\mspace{14mu} {mm}}{{D(z)}{{dz}.}}}}$

Since the dose in the patient close to the surface is higher than it isinside the patient, the weighted CTDI_(w) is used

CTDI_(w)=½CTDI₁₀₀ ^(central)+⅔CTDI₁₀₀ ^(peripher),

wherein CTDI₁₀₀ ^(central) is measured in the middle of the phantom, andCTDI₁₀₀ ^(peripher) is measured at the periphery of the phantom.

In many computed tomography devices it is possible to carry out a spiralscan. Here the examination volume is moved at a constant speed throughthe computed tomography device, while the x-ray source is rotated with aconstant angular velocity within the computed tomography device. Thex-ray source therefore moves relative to the examination volume on aspiral, in particular on a helix. A spiral scan is described by thepitch factor p, which is defined as P=d/(M·T), wherein d refers to thedistance covered by the examination volume during a complete orbit ofthe x-ray source, and wherein M is the number of rows of the x-raydetector used, and wherein T is the slice thickness. The pitch factorcan in particular assume values between 0 and 2. CTDI_(vol) is used as ameasure for the dose for a spiral scan, which is the CTDI_(w) correctedby the pitch factor, according to the following formula

${CTDI}_{vol} = {\frac{{CTDI}_{w}}{P}.}$

A reference dose parameter and/or a real dose parameter can alsocorrespond to the dose length product, abbreviated to DLP. Here the doselength product is defined in particular as the product of a computedtomography dose index with the axial length of the examination volume.

As well as the computed tomography dose index and the dose lengthproduct, the size-specific dose estimation, abbreviated to SSDE, is alsoknown. This is based on the computed tomography dose index of a computedtomography imaging and additionally relates to a water equivalentdiameter of a patient. For definition of the various dose parameters thereader is also referred in particular to the publication AmericanAssociation of Physicists in Medicine (2008): “The Measurement,Reporting, and Management of Radiation Dose in CT (Task Group 23)”, theentire contents of which are hereby incorporated herein by reference.

A topogram is in particular a two-dimensional overview recording of theexamination volume by way of x-ray radiation, it can in particularcorrespond to a two-dimensional x-ray recording, in particular to afluoroscopy recording. For recording of a topogram an examination volumecan be moved past the cone beam of the stationary tubes with the aid ofa movable table. A topogram can in particular involve an x-rayprojection relating to a projection direction. A topogram can inparticular be a lateral topogram or an anterior-posterior topogram.

FIG. 1 shows a flow diagram of a first example embodiment fordetermination of a reference dose parameter.

The first step of the first example embodiment shown is the firstreceipt REC-1 of a water equivalent diameter of a slice plane of anexamination volume via an interface 401. The water equivalent diametercan in particular have been recorded beforehand based on a topogram ofthe examination volume.

The second step of the first example embodiment shown is the firstdetermination DET-1 of a noise level based on the water equivalentdiameter via a computer unit 402, wherein the noise level is an upperthreshold value for the noise of a CT image dataset. In this exampleembodiment the noise of a CT image is defined as the standard deviationof the measured Hounsfield units of a region, which has constant realHounsfield units. This region with constant real Hounsfield units caninvolve the air shown in the image dataset, as an alternative the noisecan also always be determined by computed tomography imaging of an atleast partly homogeneous phantom. In the example embodiment shown thenoise level s is determined by the formula

s=max(c,m·WED+t)

wherein the constants are selected here as c=4 HU, m=1 HU/cm and t=−14HU. It is naturally also possible to choose different constants, inorder to comply with changed requirements for the calculation.Furthermore max(a,b) refers here to the maximum of a variable a and avariable b, in other words max(a,b)=a, if a is greater than or equal tob, and max(a,b)=b, if b is greater than a.

The next step of the first example embodiment shown is the seconddetermination DET-2 of a reference dose parameter based on the noiselevel and the water equivalent diameter via the computer unit 402,wherein the reference dose parameter corresponds to a first x-ray dose,which would be absorbed in the slice plane during a recording of a firstCT image dataset of the examination volume, if the noise of the first CTimage dataset corresponds to the noise level.

Further, in at least one embodiment, the reference dose parameter isindirectly proportional to a power of the noise level. The referencedose parameter in this example embodiment is a computed tomography doseindex, abbreviated to CTDI, in particular the CTDIvol of a spiral scan.

In the example embodiment shown the reference dose parameter iscalculated as

${{{CTDI}_{vol}\left( {{WED},s} \right)} = {k \cdot \frac{\exp \left( {l_{w} \cdot {WED}} \right)}{s}}},$

wherein here the value p of the power is precisely 1, wherein k is aproportionality constant, which in this example embodiment is chosen ask=1 mGy·HU, and l_(w) is the linear attenuation coefficient of x-rayradiation in water. Here l_(w)=0.19 cm⁻¹ is usually assumed as thelinear attenuation coefficient. As an alternative the reference doseparameter can also be calculated as

${{{CTDI}_{vol}\left( {{WED},s} \right)} = {k \cdot {\exp \left( {l_{w} \cdot {WED}} \right)} \cdot \left( \frac{s_{0}}{s} \right)^{p}}},$

wherein s₀ is a scaling factor of the noise level, wherein the unit ofthe scaling factor of the noise level is likewise an HU or Hounsfieldunit. In this case the proportionality constant k bears the unit mGy. Ifwith this alternate calculation method s₀=1 HU and p=1 is chosen, bothmethods of calculation are identical.

The next step of the example embodiment shown is the third determinationDET-3 of a size-specific dose estimation based on the reference doseparameter via the computer unit 402. This involves an optional step,which does not have to be implemented in each example embodiment of theinventive method.

The size-specific dose estimation is calculated in this exampleembodiment as

SSDE(WED,s)=f(WED)·CTDI_(vol)(WED,s),

wherein f is a function, which depends only on the water equivalentdiameter WED, but not on CTDI_(vol). The function f is given in thisexample embodiment by a table, which comprises the function values for anumber of values of the water equivalent diameter. These function valuesare often also referred to as correction factors. A function value for anon-tabulated water equivalent diameter can be determined byinterpolation, in particular by linear interpolation of two or morefunction values of tabulated water equivalent diameters.

This example embodiment can be used, during computed tomography imaging,to compare the real dose parameter, here in particular the CTDIvol,given by the real imaging, with the reference dose parameter, here theCTDIvol calculated based on the water equivalent diameter, and in thisway to assess the imaging in respect of the dose absorbed by thepatient. This assessment can in particular be undertaken without callingup or analyzing the axial image data recorded during computed tomographyimaging. Therefore this example embodiment in particular is alsosuitable for assessing a large number of computed tomography imagings,wherein the data of the computed tomography imagings is storedgeographically separated from the evaluation unit. As an alternative theassessment can also be carried out in relation to the size-specific doseestimation in each case.

TABLE A Dummy code for the first example embodiment A.1 functionnoise(WED): A.2   m = 1.0; t = −14.0; c = 4.0 A.3   return max(c,m*WED + t) A.4 function ctdi_vol(WED): A.5   k = 1.0; l_water = 0.19 A.6  return k*exp(l_water * WED) / noise(WED) A.7 function ssde(WED,cor_factors): A.8   WED_1 = lower_key(cor_factors, WED) A.9   WED_2 =upper_key(cor_factors, WED) A.10   cor_factor = (cor_factors[WED_2] −cor_factors[WED_1]) * (WED − WED_1)/ (WED_2 − WED_1) +cor_factors[WED_1] A.11   return cor_factor*WED

Table A shows dummy code for the first example embodiment. Listed incode lines A.1. A.4 and A.7 are the function declarations fordetermining the noise level, the CTDI_(vol) and the SSDE. Chosen in codelines A.2 and A.5 are the constant parameters as described for the firstexample embodiment. The code lines A.3 and A.6 correspond to the alreadydescribed formulae for determining the noise level and the CTDI_(vol).The function ssde, as well as the water equivalent diameter, also has alist cor_factors with pairs of water equivalent diameters and associatedcorrection factors passed to it. The function lower_key in the code lineA.8 enables the largest water equivalent diameter of the cor_factors tobe determined, which is still smaller than the water equivalent diameterpassed to the function. The function upper_key in the code line A.9enables the smallest water equivalent diameter of the list cor_factorsto be determined, which is still larger than the water equivalentdiameter passed to the function. At this point a further interrogationcan optionally be built in as to whether the water equivalent diameterpassed to the function is contained in the list cor_factors, and theassigned correction factor multiplied by the water equivalent diameterpassed to the function can be returned. If the interrogation isnegative, or in the listed dummy code of Table A in the code line A.10 alinear interpolation of the correction factor cor_factor is alwayscalculated, which is multiplied in code line A.11 by the waterequivalent diameter passed to the function.

FIG. 2 shows a flow diagram of a second example embodiment fordetermination of a reference dose parameter. The method steps of firstreceipt REC-1, of first determination DET-2 and of second determinationDET-3 are carried out analogously to the description of the firstexample embodiment.

A further step of the second example embodiment shown is the fourthdetermination DET-4 of a recording parameter of a computed tomographydevice 420 based on the reference dose parameter via the computer unit402, wherein a second x-ray dose corresponds to the reference doseparameter, wherein the second x-ray dose would be absorbed in the sliceplane during recording of a second CT image dataset if the second CTimage dataset is recorded using the recording parameter via the computedtomography device 420. In the example embodiment shown the recordingparameter is the x-ray current of the x-ray tubes of the computedtomography device 420. If the computed tomography device 420 comprisesmeans for dose modulation, in particular by variation of the x-raycurrent, then the recording parameter can alternately also be an averagevalue of the x-ray current of the x-ray tubes of the computed tomographydevice 420.

If the x-ray current as well as all further variables influencing thecomputed tomography (such as for example pitch factor or x-ray voltage)are predetermined, it is possible to determine the CTDI_(vol) of animaging using the x-ray current and the further variables. For examplethe CTDI_(vol) can be calculated on the basis of tabulated measurementvalues, wherein the measurement values are recorded by way of one ormore dosimeters in a phantom. If, for a specific combination of x-raycurrent and the further variables, no measurement values are tabulated,then these can be interpolated, in particular interpolated linearly.Thus in particular, if the other variables are kept constant, a functioncan be determined, which describes the CTDI_(vol) as a function of thex-ray current.

Since the x-ray dose absorbed in the examination volume is directlyproportional to the x-ray current, the CTDI_(vol) also increasesmonotonously with the x-ray current. It is therefore possible todetermine the x-ray current so that the CTDI_(vol) corresponds to thereference dose parameter, in that the reciprocal function is determined,which describes the x-ray current as a function of the CTDI_(vol). Thedetermination of the reciprocal function can in particular also becarried out graphically or numerically, so that it is not necessary toknow the original function term.

TABLE B Dummy code for the third example embodiment B.1 functionxray_current_it(ctdi_vol, imaging_params,     current_lower,current_upper): B.2   ctdi_vol_calc_lower =    scanner.ctdi_vol(imaging_params, current_lower) B.3  ctdi_vol_calc_upper =     scanner.ctdi_vol(imaging_params,current_upper) B.4   current_mid = (current_lower + current_upper)/2 B.5  ctdi_vol_calc_mid =     scanner.ctdi_vol(xray_current, current_mid)B.6   if abs(ctdi_vol_calc_mid − ctdi_vol)/ ctdi_vol < 0.01: B.7    return current_mid B.8   else if ctdi_vol_calc_mid > ctdi_vol: B.9    return xray_current_it(ctdi_vol, imaging_params,      current_lower, current_mid) B.10   else: B.11     returnxray_current_it(ctdi_vol, imaging_params,       current_mid,current_upper) B.12 function xray_current(WED, imaging_params): B.13  ctdi_vol_ref = ctdi_vol(WED) B.14   current_max =scanner.xray_current_max B.15   return xray_current_it(ctdi_vol_ref,imaging_params,     0. current_max)

Table B shows dummy code for the second example embodiment. Defined inthe code lines B.1 . . . , B.11 is a function for iterativedetermination of the x-ray current, which is based on the bisectionmethod. Defined in the code lines B.12, . . . , B.15 is a function fordetermining the x-ray current based on the water equivalent diameter WEDand the further variables imaging_params.

In code line B.13 the reference CTDI_(vol) is calculated by way of thefunction defined in Table A. Called in code line B.14 is the maximumx-ray current current_max of the scanner. Code line B.15 calls theiterative function for determining the x-ray current.

Calculated in code lines B.2 and B.3 by way of a function made availableby the scanner is the CTDI_(vol), wherein two different x-ray currentscurrent_lower and current_upper are used, so that the CTDI_(vol) in thefirst case is smaller than the reference CTDI_(vol) and in the secondcase is larger than the reference CTDI_(vol). The function madeavailable by the scanner for calculating the CTDI_(vol) calculates thesedose parameters as a function of the given recording parameters.

Determined in code line B.4 is a further x-ray current current_mid asthe mid value of the x-ray currents current_lower and current_upper,furthermore in code line B.5 the CTDI_(vol) for this x-ray current isdetermined.

If the CTDI_(vol) for the mid value of the x-ray currents current_lowerand current_upper is close enough to the reference CTDI_(vol) (in thedummy code shown here, when the relative deviation is less than 1percent), this mid value of the x-ray current is returned in code lineB.6 and B.7. Otherwise the function is called iteratively in code linesB.8, . . . , B.11, wherein the function parameters of the x-ray currentsare determined based on the CTDI_(vol) at the mid value of the x-raycurrent.

FIG. 3 shows a flow diagram of a third example embodiment fordetermination of a reference dose parameter. The method steps of firstreceipt REC-1, first determination DET-2 and of second determinationDET-3 are carried out analogously to the description of the firstexample embodiment.

Furthermore in the third example embodiment there is a second receiptREC-2 of a real dose parameter of a recording of a third CT imagedataset of the examination volume via the interface 401. wherein thereal dose parameter corresponds to the third x-ray dose absorbed in theslice plane during the recording of the third CT image dataset.Furthermore in the second receipt REC-2 the noise level of the third CTimage dataset is also received.

Furthermore in the third example embodiment there is a correction COR ofthe power and/or the proportionality constant based on a comparison ofthe reference dose parameter and the real dose parameter via thecomputer unit 402. A correction can in particular be realized byadaptation of the function equation, in which the power and/or theproportionality constant are entered as fit parameters. The adaptationof a function equation can be carried out in particular by way of theLevenberg-Marquardt algorithm. The function equation can in particularbe given by the function CTDI_(vol)(WED,s) defined in the informationfor the first example embodiment. Further pairs of reference doseparameters and real dose parameters can in particular also be includedin the adaptation of the function equation.

The third example embodiment shown is advantageous in particular if thepower and/or the proportionality constant have to be chosen separatelyfor various computed tomography devices or different manufacturers ineach case.

FIG. 4 shows a parameter determination unit 400 for determining areference dose parameter. The parameter determination unit 400 shownhere is designed to carry out an embodiment of the inventive method.This parameter determination unit 400 comprises an interface 401, acomputer unit 402, a memory unit 403 and also an input and output unit404.

The parameter determination unit 400 can in particular involve acomputer, a microcontroller or an integrated circuit. As an alternativethe parameter determination unit 400 can involve a real or virtualnetwork of computers (a real network is known as a cluster, a virtualnetwork is known as a Cloud).

An interface 401 can involve a hardware or software interface (forexample PCI bus, USB or Firewire). A computer unit 402 can have hardwareelements or software elements, for example a microprocessor or aso-called FPGA (Field Programmable Gate Array). A memory unit 403 can berealized as Random Access Memory (RAM) or as permanent mass storage(hard disk, USB stick, SD card, solid state disk). An input and outputunit 404 comprises at least one input unit and/or at least one outputunit.

FIG. 5 shows an example embodiment of a possible incorporation of aparameter determination unit 400 into an environment for distributedcomputing. The parameter determination unit is connected via a network540 to a server 500, which for its part is connected to a database 520.

A server 500 can in particular involve a computer, a microcontroller oran integrated circuit. As an alternative the server 500 can involve areal or virtual network of computers (a real network is known as acluster, a virtual network is known as a Cloud).

The server comprises a server interface 501 and a server computer unit502. A server interface 501 can involve a hardware or software interface(for example PCI bus, USB or Firewire). A server computer unit 502 canhave hardware elements or software elements, for example amicroprocessor or a so-called FPGA (Field Programmable Gate Array).

The database 520 can be realized in a memory of the server 500, but itcan also be embodied, as in the example embodiment shown, as a separatedatabase server. The database 520 comprises a plurality of examinationdatasets 530.1. 530.2, each of the examination datasets 530.1. 520.2comprises a topogram recording 531.1. 531.2 of an examination region andalso one or more image series 532.1. 532.2 comprising axial slice imagesof the examination region.

A network 540 can involve a local area network, abbreviated to LAN, or awide area network, abbreviated to WAN. An example for a LAN is anintranet, an example for a WAN is the Internet. The connection is suchcases can be made via cables (for example via Ethernet, PowerLAN orTokenRing), as an alternative the connection can also be wireless (forexample via a wireless local area network, abbreviated to WLAN, orinfrared or Bluetooth). In the example embodiment shown the network 540corresponds to the Internet.

In the example embodiment shown the server 500 and the database 520 arepart of an architecture for distributed computing. The database 520stores data from a large number of computed tomography imagings, theserver 500 regulates the access to the database 520. As in the firstexample embodiment, the reference value of the CTDIvol and/or of theSSDE is to be calculated from the plurality of computed tomographyimagings.

It is known from the prior art that the series of images 532.1. 532.2 ofthe examination datasets 530.1. 530.2 can be transmitted via the network540 to the parameter determination unit, in order to calculate from theseries of images 532.1. 532.2 comprising axial slice images therespective CTDIvol and/or the SSDE. The calculation on the basis of theaxial slice images is slow however, also high volumes of data must betransmitted via the restricted bandwidth of the network 540.

In the example embodiment of the present invention shown only at leastone topogram recording 531.1. 531.2 is transmitted via the network 540to the parameter determination unit 400, but no series of images 532.1.532.2 comprising axial slice images however. From a topogram recording531.1. 531.2 a water equivalent parameter of a slice plane can bedetermined, in that the topogram recording 531.1. 531.2 is compared toreference topogram recordings, for which in each case the waterequivalent diameter is known, or by way of a threshold valuesegmentation. Using the flow diagram shown in FIG. 1, the optimumCTDIvol of the respective recording can then be calculated, and thisreference dose parameter can be used for statistics over many computedtomography imagings.

The patent claims of the application are formulation proposals withoutprejudice for obtaining more extensive patent protection. The applicantreserves the right to claim even further combinations of featurespreviously disclosed only in the description and/or drawings.

References back that are used in dependent claims indicate the furtherembodiment of the subject matter of the main claim by way of thefeatures of the respective dependent claim; they should not beunderstood as dispensing with obtaining independent protection of thesubject matter for the combinations of features in the referred-backdependent claims. Furthermore, with regard to interpreting the claims,where a feature is concretized in more specific detail in a subordinateclaim, it should be assumed that such a restriction is not present inthe respective preceding claims.

Since the subject matter of the dependent claims in relation to theprior art on the priority date may form separate and independentinventions, the applicant reserves the right to make them the subjectmatter of independent claims or divisional declarations. They mayfurthermore also contain independent inventions which have aconfiguration that is independent of the subject matters of thepreceding dependent claims.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for” or,in the case of a method claim, using the phrases “operation for” or“step for.”

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A method for determining a reference doseparameter of computed tomography imaging, comprising: receiving, via aninterface, a water equivalent diameter of a slice plane of anexamination volume; determining, via a computer unit, a noise levelbased on the water equivalent diameter, the noise level being an upperthreshold value for noise of a CT image dataset; determining, via thecomputer unit, a reference dose parameter based on the noise leveldetermined and the water equivalent diameter, the reference doseparameter corresponding to a first x-ray dose, absorbable in the sliceplane during a recording of a first CT image dataset of the examinationvolume upon noise of the first CT image dataset corresponding to thenoise level determined, and the reference dose parameter beingindirectly proportional to a power of the noise level determined.
 2. Themethod of claim 1, wherein the power has a value of between 0.1 and 2.5.3. The method of claim 1, wherein the reference dose parameter isfurther proportional to an exponential function of the water equivalentdiameter.
 4. The method of claim 3, wherein an argument of theexponential function includes a product of a linear attenuationcoefficient of x-ray radiation in water with the water equivalentdiameter.
 5. The method of claim 3, wherein the reference dose parameteris a product of a proportionality constant with a quotient of anexponential function and the power of the noise level, wherein p is avalue of the power, wherein the proportionality constant is between 0.2mGy·HU^(p) and 2.0 mGy·HU^(p).
 6. The method of claim 1, wherein thenoise level is a piecewise linear function of the water equivalentdiameter.
 7. The method of claim 6, wherein the noise level is acontinuous sectionally-defined function of the water equivalent diameterwith a first section and a second section, wherein the first section isa constant function and wherein the second section is a linear functionof the water equivalent diameter.
 8. The method of claim 1, furthercomprising: determining, via the computer unit, a size-specific doseestimation based on the reference dose parameter.
 9. The method of claim1, further comprising: determining, via the computer unit, a recordingparameter of a computed tomography device based on the reference doseparameter, wherein a second x-ray dose corresponds to the reference doseparameter, and wherein the second x-ray dose is absorbable in the sliceplane during recording of a second CT image dataset upon the second CTimage dataset being recorded using the recording parameter.
 10. Themethod of claim 5, further comprising: receiving, via the interface, areal dose parameter of a recording of a third CT image dataset of theexamination volume, wherein the real dose parameter corresponds to athird x-ray dose absorbed in the slice plane during the recording of thethird CT image dataset; and correcting at least one of the power and theproportionality constant based on a comparison, via the computer unit,of the reference dose parameter and the real dose parameter.
 11. Aparameter determination unit, comprising: an interface, embodied toreceive a water equivalent diameter of a slice plane of an examinationvolume; and a computer unit, embodied to determine a noise level basedon the water equivalent diameter, the noise level being an upperthreshold value for noise of a CT image dataset, and determine areference dose parameter based on the noise level and the waterequivalent diameter, the reference dose parameter corresponding to afirst x-ray dose, absorbable in a slice plane during a recording of afirst CT image dataset of the examination volume upon the noise of thefirst CT image dataset corresponding to the noise level, and thereference dose parameter being indirectly proportional to a power of thenoise level.
 12. The parameter determination unit of claim 11, whereinthe power has a value of between 0.1 and 2.5.
 13. A computed tomographydevice comprising: the parameter determination unit of claim
 11. 14. Anon-transitory computer program product including a computer program,directly loadable into a memory of a parameter determination unit,including program sections to carry out the method of claim 1 when theprogram sections are executed by the parameter determination unit.
 15. Anon-transitory computer-readable storage medium, storing programsections readable and executable by a parameter determination unit, tocarry out the method of claim 1 when the program sections are executedby the parameter determination unit.
 16. The method of claim 2, whereinthe power has a value of between 0.5 and 1.5.
 17. The method of claim16, wherein the power has a value of between between 0.9 and 1.1. 18.The method of claim 5, wherein the proportionality constant is betweenbetween 0.5 mGy·HU^(p) and 1.5 mGy·HU^(p).
 19. The method of claim 18,wherein proportionality constant is between 1.2 mGy·HU^(p) and 1.2mGy·HU^(p).
 20. The method of claim 4, wherein the reference doseparameter is a product of a proportionality constant with a quotient ofan exponential function and the power of the noise level, wherein p is avalue of the power, wherein the proportionality constant is between 0.2mGy·HU^(p) and 2.0 mGy·HU^(p).
 21. A computed tomography devicecomprising: the parameter determination unit of claim 12.